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-CONFIGURATION OPTIONS
There are a number of configuration options possible on the ZPB
that are specified by wiring jumpers on the board.
The desired
configuration should be wired according to the following
instructions before the board is used.
Jl. -Signal grounding. Backplane pins 20 and 70 may be optionally
connected to ground.
These connections can be made by
in~talling
the jumpers labeled "EC20" and "EC70",
respectively, located at 6A.
These connections should be
made unless these grounds would interfere with the operation
of other boards on the bus.
Grounding these pins will
reduce backplane noise and thus provide more reliable
per formance. , Both pins should be grounded with a HORI ZON.
Pin 20 should not be grounded for use with the IMSAI.
Neither pin should be grounded on an Altair.
Memory wait states. The "lW" jumper to the right of location
7G, if connected, forces at least one wait state on every
memory or I/O reference made by the processor.
(If a memory
board specifies one or more wait states, then that number of
wait states will be used for references to that board.)
The
jumper should be installed if memory in the system is not
fast enough to run with zero wait states at 4MHz (about
300ns or faster) and the memory itself cannot be configured
to have one wait state.
If you are not sure your memories
are this fast, connect the jumper to get the system running
and experiment later.
The North Star 16K RAM Board does not
require any wait states.
Processor speed. Normally the processor runs at 4MHz.
However, provision has been made to run at 2MHz.
To achieve
2MHz operation,
r~place
the 8MHz crystal at location IF with
a 4MHz crystal (not supplied).
Then cut the "4" trace above
location 6F and install the "2" jumper instead.
This keeps
the clock on backplane pin 49 at 2MHz as required by some S-
100 bus boards.
-Address mirror ing. As required by some S-100 bus
boards~,
the
ZPB simulates an 8080 during IN and OUT instructions by"·
driving the port address onto both 8-bit halves of the
address bus.
To disable this feature and take advantage of
the greater flexiblility of the Z80, cut the "AM" (address
mirror) trace to the left of location 7F and install the
"NM" (no mirror) jumper instead.
-Control panel. The ZPB normally generates the MWRITE signal
to backplane pin 68.
If the ZPB is used in systems with
control panels or other boards that generate MWRITE, then
the "MW" trace below location 6B should be cut.
Leave the
trace in place for use in the HORIZON.
Cut the trace when
used with an Altair or IMSAI.
I
21
-North Star Z80A PROCESSOR BOARD
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